Is javascript method overloading allowed?

I have a function:

function bla(param1) {
    // do stuff
}

If I change this to:

function bla(param1, param2) {
    // do stuff
}

Will this affect how the function works? I.e. Can I run this function like this:

function("one");

AND like this:

function ("one", "two");

Will both work in all cases? And if so, will the second parameter just be null?